The invention relates to a method for wrapping a rubber strip around a forming drum in the manufacture of a pneumatic tire and a wrapping apparatus, and more particularly to a method for wrapping a rubber strip and a wrapping apparatus in which an accuracy of wrapping the rubber strip is improved.
As a method for manufacturing the pneumatic tire, a process including the steps of supplying an unvulcanized rubber strip from an injection device continuously, wrapping the rubber strip around the forming drum and forming tire-constituting members such as a cap tread, an under tread, a side tread and a rim cushion rubber part based on a laminated structure of the rubber strip is performed.
There have been advantages by forming the tire-constituting members directly in such manner as described above that manufacturing efficiency of the tire can be improved, as well as space savings can be realized since the tire-constituting members formed in advance are not stored, and, as a result, manufacturing cost of the tire can be reduced.
However, it has been extremely difficult to wrap around the forming drum with high accuracy since the rubber strip in an initial stage extruded from the injection device tends to result in overshoot and thus unstable output. In such manner as described above, when the accuracy of wrapping the rubber strip is inferior, quality of the pneumatic tire becomes unstable.
The object of the invention is to provide a method for wrapping a rubber strip and a wrapping device in which variation in an amount of extrusion of the rubber strip is absorbed between the injection device and the forming drum, whereby the rubber strip can be wrapped with the high accuracy.
A method for wrapping rubber strip according to the invention for accomplishing the object described above is a method for wrapping a rubber strip around a forming drum while extruding an unvulcanized rubber strip from an injection device comprises the steps of:
pressing the rubber strip by a guide roll against the forming drum under tension while forming a space for absorbing variations in an amount of extrusion of the rubber strip between the guide roll and an extrusion outlet of the injection device;
rotating the forming drum in synchronism with extrusion of the rubber strip so that the guide roll is driven; and
wrapping the rubber strip guided by the guide roll around the forming drum,
In such manner as described above, since the rubber strip is pressed by the guide roll against the forming drum under tension while a space is formed for absorbing variations in the amount of extrusion of the rubber strip between the guide roll and the extrusion outlet of the injection device, even though the amount of extrusion of the rubber strip is unstable at an initial stage of extrusion, variations in the amount of extrusion can be absorbed in the space. Therefore, the rubber strip guided by the guide roll can be wrapped around the forming drum with high accuracy. Moreover, an excellent guiding function is shown and the accuracy of wrapping further is improved, when an angle of contact between the guide roll and the rubber strip is sufficiently large.
On the other hand, a device for wrapping a rubber strip according to the invention for accomplishing the object described above is a device for wrapping a rubber strip around a forming drum while extruding an unvulcanized rubber strip from an injection device, that comprises a guide roll arranged between the injection device and the forming drum through a freely stretchable and contractible arm member along a supplying channel for the rubber strip, wherein the rubber strip is pressed by the guide roll against the forming drum under tension when the arm is stretched, as well as a space for absorbing variations in an amount of extrusion of the rubber strip is formed between the guide roll and an extrusion outlet of the injection device.
In the invention, it is preferable that the guide roll is released from the forming drum at a final stage of wrapping of the rubber strip to form a clearance between the forming drum and the guide roll, and the rubber strip is cut off within the clearance. The rubber strip is cut off within the clearance as described above, whereby a subsequent wrapping operation can be performed successively, since the cut end of the rubber strip still remains on the guide roll. Moreover, tension is applied to the rubber strip from an initial stage of wrapping at the subsequent wrapping operation, whereby the rubber strip can be wrapped with high accuracy. As such a device in this case, a cutting device which cuts off the rubber strip within a clearance can be provided and the clearance arranged between the forming drum and the guide roll when the arm member is contracted.
Moreover, a press roll for pressing the cut end of the rubber strip against the forming drum can be provided at the vicinity of the guide roll when the cut end is pressed against the forming drum by the press roll and disarrangement of the out end of the rubber strip is prevented.